Health campaigners are furious that the former head of HM Revenue and Customs has taken a role with a powerful lobbying organisation that campaigns against tobacco taxation. Dave Hartnett, who stepped down as permanent secretary of tax at HMRC in 2012, became a director of the International Tax and Investment Center (Itic), a Washington-based organisation that is accused of promoting the interests of “big tobacco”, in 2013.

Clear the Air, a Hong Kong pressure group, said Harnett should have declared the role. The advisory committee on business appointments (Acoba) has confirmed that he did not seek its permission, as would normally happen when a senior civil servant takes a prominent role within two years of leaving Whitehall. Hartnett insists that he did not need permission for the unpaid role as nominal director. “I do not believe there was anything here to report to Acoba and it follows that I do not believe that I have offended the letter or spirit of the Acoba rules,” he said in a statement.

Documents show Hartnett chaired meetings for Itic in October 2013. He has also given talks and is due to speak at one of its conferences next month.

Itic boasts that its sponsors have the opportunity to “gain special access to partner country policy-makers and legislators”, but it is regularly accused of undermining health legislation. According to TobaccoTactics.org, it is funded by multinational corporations, including industry leaders Philip Morris, Japan Tobacco International, British American Tobacco and Imperial Tobacco. All four companies have representatives on Itic’s board of directors.

Internal documents obtained by The Observer show how PMI intended to use Itic to lobby against the UK’s plan for plain packaging for cigarettes, seen by health campaigners as a major weapon in the fight to stop young people taking up smoking.

“Itic is paid by the tobacco industry to lobby governments against policies to cut smoking,” said Deborah Arnott, chief executive of health charity ASH. “I’m shocked that Mr Hartnett seems to be happy to allow his status as a former permanent secretary to be used by a tobacco industry front group that promotes addiction, disease and premature death.”

Daniel Witt, president of Itic, defended his organisation, saying it provides a “neutral forum for discussions on tax and investment policy”. Supporters of Itic deny claims that it is in the pocket of big tobacco.

However major health organisations are critical of the way it operates.

The UK is a signatory to the World Health Organisation’s framework convention on tobacco control, which was established to check the influence of tobacco companies and their front organisations. In an unusual move, the organisation has openly called for governments to distance themselves from Itic.

“Itic has published extensively in favour of the tobacco industry’s false positions on excise taxation, investment and illicit trade in tobacco products,” said Dr Douglas Bettcher, director of prevention of noncommunicable diseases for the WHO. “Itic have used their international conferences, such as in Moscow in 2014 and in New Delhi earlier this month, to lobby government officials against tobacco taxation. This is despite tobacco taxation being the most effective and efficient measure to reduce demand for tobacco products. Parties to the WHO framework convention on tobacco control are obliged to protect their public health policies from interference by the tobacco industry and its allies. In this light, WHO urges all countries to follow a non-engagement policy with Itic.”

Hartnett attracted controversy after negotiating tax deals with major corporations such as Vodafone and Goldman Sachs. Critics said the deals were generous to the companies, a claim rejected by HMRC. Since stepping down from the civil service, he has come under fire for his advisory work with HSBC.

Concerns about Itic recently prompted the World Bank to pull out of a tax conference that was funded by several of its transnational tobacco company supporters. “For over two decades Itic has promoted tobacco-friendly fiscal policies in developing countries that have helped fuel the global tobacco epidemic, but governments and international organizations like the World Bank are increasingly realising that Itic is nothing more than a secret mouthpiece for big tobacco companies,” said Matt Myers, president of the Campaign for Tobacco-Free Kids.

In a statement to the Observer, Hartnett explained that he was, along with around 50 other “leading figures in taxation”, a nominal director of Itic.

“I am not paid for that role,” Hartnett said. “I am not an executive director and do not in any way direct the strategy or business of Itic. I know Itic as a not-for-profit research and education organisation which supports the development of tax systems in less developed countries.”

Sheila Duffy, chief executive of ASH Scotland, called on the government to confirm whether any rules had been breached.

“I’d also like to see HMRC and other government departments ensure that no current public official confers any appearance of legitimacy on Itic.”